On this page
Most students know Dolly the sheep as a famous name. Fewer can explain what was actually new about her, which is the part an exam or a debate will test. This post covers who Ian Wilmut was, how Dolly was made, what her birth proved, and the common confusions about clones.
Who was Ian Wilmut?
The Roslin Institute's obituary says Professor Sir Ian Wilmut died in 2023 at the age of 79. He was born near Stratford-upon-Avon, became interested in biology at school in Scarborough, and went to the University of Nottingham to study agriculture before switching to animal science. His PhD and fellowship at the University of Cambridge were on freezing semen and embryos, work that led to Frostie, the first calf born from a frozen embryo.
He then moved to the Animal Breeding Research Organisation near Edinburgh, which became the Roslin Institute. There he worked on genetically modified sheep that could produce human medicinal proteins in their milk. That project needed a more efficient way to make such sheep, and he led the effort to develop cloning by nuclear transfer. The obituary lists the results: Megan and Morag in 1995, Dolly in 1996, and Polly, the first mammal both cloned and genetically modified, in 1997. He was knighted in 2008 and retired from the University of Edinburgh in 2012.
How was Dolly made?
The Roslin Institute's page on Dolly's life gives the recipe. A cell was taken from the mammary gland of a six-year-old Finn Dorset sheep. An egg cell was taken from a Scottish Blackface sheep. The method, explained on the institute's cloning FAQ, is somatic cell nuclear transfer: the egg's own nucleus is removed and replaced with the nucleus of the adult donor cell. The embryo was carried by a Scottish Blackface surrogate, and Dolly was born on 5 July 1996.
Her white face was an early clue. A Scottish Blackface has a black face, so if Dolly had been related to her surrogate mother she would have had one too.
The team reported the work in Nature in 1997 as Viable offspring derived from fetal and adult mammalian cells, by Wilmut, Schnieke, McWhir, Kind and Campbell. The abstract states the key conclusion: a lamb derived from an adult cell "confirms that differentiation of that cell did not involve the irreversible modification of genetic material required for development to term."
A worked example: whose DNA does a clone carry?
The cloning FAQ says that about 99.9 per cent of a cell's DNA is in the nucleus as chromosomes, and about 0.1 per cent is in the mitochondria. Use that to answer a typical question.
Question: In nuclear transfer, the nucleus comes from sheep A (Finn Dorset) and the enucleated egg from sheep B (Blackface). Roughly what share of the clone's DNA comes from each?
The nucleus, from A, carries about 99.9% of the DNA.
The egg's cytoplasm, from B, still contains B's mitochondria, carrying about 0.1%.
So the clone shares almost all of its DNA with A, but not quite all of it.
The surrogate mother, if she is a third sheep, contributes no DNA at all; she only carries the pregnancy.
Common mistakes:
"A clone is an identical twin of the same age." Dolly was born in 1996 from a donor that was already six years old. Same nuclear genes, different birth date.
"The surrogate is the genetic mother." The white face shows she was not.
"Cloning is efficient." The Roslin FAQ says the technique has a very low success rate, because cloned embryos are more likely to be lost during pregnancy. The institute no longer clones animals.
What happened to Dolly?
According to the Roslin page, Dolly had six lambs, the first, Bonnie, born in April 1998. She was treated for arthritis in 2001. She was later found to have been infected by Jaagsiekte sheep retrovirus, which causes lung cancer in sheep and had infected other sheep at the institute in the same outbreak. When tumours were found in her lungs, she was put to sleep on 14 February 2003, at the age of six. Her body is in the National Museum of Scotland.
The Roslin page on stem cells adds the next chapter: Shinya Yamanaka's group announced induced pluripotent stem cells in 2006, reprogramming adult cells without an egg, and he shared the 2012 Nobel Prize for it. Our post on Shinya Yamanaka and stem cells picks up the story.
What can a student take from his way of working?
A side road can lead to the big result. Wilmut's cloning work began as a way to make better genetically modified sheep, and it ended up answering a basic question about cells.
Build on your earlier skills. His PhD on freezing embryos gave him the embryo-handling experience that nuclear transfer needed.
Big results take big teams. The Roslin page notes the team included scientists, embryologists, surgeons, vets and farm staff.
If the steps of nuclear transfer are hard to keep straight, Fermi's AI tutor can draw the figure as it explains and check your understanding as it goes. For the lab techniques behind modern biotechnology, see our guide to biotechnology principles for NEET.
Try this: sketch nuclear transfer in four boxes, labelling which sheep supplies the nucleus, the egg and the womb.
